Convert snmp octet string to human readable date f

问题:

Using the pysnmp framework i get some values doing a snmp walk. Unfortunately for the oid

1.3.6.1.21.69.1.5.8.1.2 (DOCS-CABLE-DEVICE-MIB)

i get a weird result which i cant correctly print here since it contains ascii chars like BEL ACK

When doing a repr i get:

OctetString('\x07\xd8\t\x17\x03\x184\x00')

But the output should look like:

2008-9-23,3:24:52.0

the format is called "DateAndTime". How can i translate the OctetString output to a "human readable" date/time ?

回答1:

The format is here.

A date-time specification. 
            field  octets  contents                  range
            -----  ------  --------                  -----
              1      1-2   year*                     0..65536
              2       3    month                     1..12
              3       4    day                       1..31
              4       5    hour                      0..23
              5       6    minutes                   0..59
              6       7    seconds                   0..60
                           (use 60 for leap-second)
              7       8    deci-seconds              0..9
              8       9    direction from UTC        '+' / '-'
              9      10    hours from UTC*           0..13
             10      11    minutes from UTC          0..59
* Notes:
            - the value of year is in network-byte order
            - daylight saving time in New Zealand is +13 For example, 
              Tuesday May 26, 1992 at 1:30:15 PM EDT would be displayed as:
                 1992-5-26,13:30:15.0,-4:0 
              Note that if only local time is known, then timezone
              information (fields 8-10) is not present.

You can use struct.unpack:

>>> import struct, datetime
>>> s = '\x07\xd8\t\x17\x03\x184\x00'
>>> datetime.datetime(*struct.unpack('>HBBBBBB', s))
datetime.datetime(2008, 9, 23, 3, 24, 52)

回答2:

@Paulo Scardine: This was the best answer I found online when working to resolve a very similar problem. It still took me a little while to resolve my issue even with this answer, so I wanted to post a follow up answer that may add more clarity. (specifically the issue with the date having different length options).

The following piece of code connects to a server and grabs the system time and then outputs it as a string to illustrate the method.

import netsnmp
import struct
oid = netsnmp.Varbind('hrSystemDate.0')
resp = netsnmp.snmpget(oid, Version=1, DestHost='<ip>', Community='public')
oct = str(resp[0])
# hrSystemDate can be either 8 or 11 units in length.
oct_len = len(oct)
fmt_mapping = dict({8:'>HBBBBBB', 11:'>HBBBBBBcBB'})
if oct_len == 8 or oct_len == 11:
    t = struct.unpack(fmt_mapping[oct_len], oct)
    print 'date tuple: %s' % (repr(t))
else:
    print 'invalid date format'

I hope this helps other people who are having similar issues trying to work with this type of data.

回答3:

Shameless plug here: The Pycopia SNMP and SMI modules correctly handle this object, and others as well. Pycopia is installed from source, and dont forget the mibs file if you try it.